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Top Quark Properties at the Tevatron

Top Quark Properties at the Tevatron. Florencia Canelli. on behalf of the CDF and D  collaborations April 17, 2005. Top Quark at the Tevatron. Fermilab Tevatron: World’s highest particle energy collisions ~4 miles circumference protons-antiprotons Run I (1992-1996) s = 1.8 TeV

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Top Quark Properties at the Tevatron

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  1. Top Quark Properties at the Tevatron Florencia Canelli on behalf of the CDF and D collaborations April 17, 2005

  2. Top Quark at the Tevatron • Fermilab Tevatron: • World’s highest particle energy collisions • ~4 miles circumference protons-antiprotons • Run I (1992-1996) • s = 1.8 TeV • Discover top quark in 1994! • Integrated luminosity 120 pb-1 • Run II (2001-present) • s = 1.96 TeV • Integrated luminosity by April, 05: • In tape ~600pb-1 • Analyzed up to ~350 pb-1 • 2 multi-purpose detectors • D and CDF World’s only top factory! Florencia Canelli - UCLA

  3. Run II Detectors • Inner Silicon Tracking • Tracking Chambers • Solenoid • EM and Hadronic Calorimeters • Muon Detectors Florencia Canelli - UCLA

  4. 5 orders of magnitude 12 orders of magnitude for the fundamental SM fermions!!!! Top Quark Physics • Top is very massive => It probes physics at much higher energy scale than the other fermions. • Top decays before hadronizing => momentum and spin information is passed to its decay products. No hadron spectroscopy. • Top mass constrains the Higgs mass => Mtop, enters as a parameter in the calculation of radiative corrections to other Standard Model observables it is also related, along with the mass of the W boson, to the that of the Higgsboson. Mtop (Run I world average)= 178  4.3 GeV top ~ 10-24 sec Florencia Canelli - UCLA

  5. g g ~85% ~15% Top Quark Production • In proton-antiproton collisions at TeVatron energies, top quarks are primarily produced in pairsvia the strong interactions. ~ one top event every 10 BILLION inelastic collisions Florencia Canelli - UCLA

  6. Top Quark Decay Br(t  Wb) ~ 100% • Mtop > MW decays to real Ws • Final state is given by W+ and W- decays Br(W  leptons) = 1/3 Br(W  quarks) = 2/3 jets  e • Excellent branching ratio • Large Signal/Background all-jets lepton+jets e jets lepton+jets dilepton • Larger branching ratio • Reasonable Signal/Background • Over-constrained kinematics • Less statistics • Excellent S/B • Under constrained kinematics Florencia Canelli - UCLA

  7. The Top Properties Tour Top Width Top Charge W helicity Top Spin Top Mass CP Violation Anomalous Couplings Production Kinematics Production X-Section Top Spin Polarization Resonance Production Y |Vtb| Rare/non SM decays Branching Fractions Florencia Canelli - UCLA

  8. In this Talk W helicity Top Mass Top Spin Polarization Resonance Production Florencia Canelli - UCLA

  9. q q e n Event Topology • Energetic, central, and spherical • Missing transverse energy (ET) from neutrino in lepton+jets and dilepton modes • High transverse energy, ET, jets • Two b-jets • Possible additional jets from gluon radiation (ISR, FSR) • Events are busy: • need to reconstruct parton level to measure top properties • different ways to assign jets to partons • General characteristics of the background: • No neutrinos, less ET • No b-jets • Leptons could be fakes (less isolated) • Less central Florencia Canelli - UCLA

  10. B hadrons are long-lived Vertex of displaced tracks Tagging b-jets • Use different properties of the B hadrons to identify (tag) them • Reduce backgrounds from light-quark/gluon jets • Reduce combinatorics effects 60% 0.5% Top Event Tagging Efficiency False Tag Rate (QCD jets) Florencia Canelli - UCLA

  11. Jet Energy Scale (JES) • Determine the true parton energy from measured jet energy in a cone Complex detector properties Algorithms with complex behavior such as cone, cone-midpoint, KT Need to correct for detector, algorithm and physics effects to obtain the true energy of the jets: Jet Energy Scale (JES) Complex underlying physics Florencia Canelli - UCLA

  12. Fractional Systematic Uncertainty vs PT Run I Run II 2004 Central  region Jet Energy Scale Systematic Uncertainty • How well do we know the energy of the jets (or quarks)? • Events with lots of jets => dominant uncertainty for some top analyses, i.e, top mass in lepton+jets channel. • Also expect significant improvements from D very soon. Run II 2005 ~3% jet PT uncertainty in top events ~factor of 2 decrease! Florencia Canelli - UCLA

  13. Top Quark Mass Measurements

  14. Publishing Top Quark Masses for 15 years Florencia Canelli - UCLA

  15. Top Quark Mass Weight in average 6% 7% 22% 58% 7% Mtop all-jets D result is not included in TeVatron average: Mtop = 178.015.7 GeV/c2 mH (GeV) Florencia Canelli - UCLA

  16. Measuring the Top Quark Mass • Run II began in March 2001: • take data, commissioning detectors, • calibrate detectors, • tune Monte Carlo and detector simulation, • prepare analysis • By the end of 2004 after 3 years of Run II running the top mass measurement did not reach to Run I precision (~5.1 GeV) • Better precision comes from l+jets (golden channel), but are we looking at the same top among channels? • By the end of Run I, the JES uncertainty was as large as the statistical uncertainty ~3.5 GeV • Different methods: try to optimize the statistical and systematic performance Results by the end of 2004 Two different techniques: Template and Matrix Element based Florencia Canelli - UCLA

  17. Template Technique • Determine mass of the top quark using a quantity strongly dependent on the top quark mass Mtop (usually Reconstructed Mtop) • Determine the Reconstructed Mtop per event: Minimize a 2 expression for the resolutions and kinematic relationships in the ttbar system. Choose jet to parton assignment and Pz based on best fit quality. Build signal and background templates • Obtain the measurement from the data: Compare Reconstructed Mtop from data with same from randomly generated and simulated signal at various input top mass (Mtop) and backgrounds using an unbinned likelihood fit Signal Template Background Template Data Best signal + background templates to fit the data L = Lshape x Lbackground Florencia Canelli - UCLA

  18. Template Analysis at CDF • Improve statistical power of the method dividing the sample in 4 subsamples that have different background contamination and different sensitivity to the top mass • Extend 1-D template (only on Reconstructed Mtop) to maximize sensitivity to JES: • Mtop and JES are simultaneously determined in likelihood fit using shape comparisons of Reconstructed Mtop and, Reconstructed Mjjdistributions, taking correlations between them • Use a priori CDF information on JES (page 8): JES Gaussian constraint (mean=0, width=1) Florencia Canelli - UCLA

  19. Template Results from CDF Combined–Log(L) Expected error NEW Florencia Canelli - UCLA

  20. Template Results from CDF Systematic uncertainties Measurement is more precise than the current world average! –Log Likelihood vs Mtop, JES JES(s) Most of these can be reduced with more data Mtop (GeV) Florencia Canelli - UCLA

  21. Template Results from D • Topological • No b-tagging requirement • Construct a discriminant using topological variables (DLB) to improve S/B • At least one b-tagged jet: • no requirement on discriminant DLB • First top mass at D top mass measurement with b-tagging ttbar candidates 69 S/B~3/1 Reconstructed Mtop (GeV) ttbar candidates 94 S/B~1/1 Reconstructed Mtop (GeV) Florencia Canelli - UCLA

  22. Matrix Element Technique • Determine mass of the top quark evaluating a probability using all the variables in the event, integrate over all unknowns • Sum over all permutations of jets and neutrino solutions • Background process probabilities are or not be explicitly included in the likelihood • Top mass: maximizei Pi (x;Mtop) • Each event has its own probability • Correct permutation is always considered (along with the other eleven) • All features of individual events are included, thereby well measured events contribute more information than poorly measured events W(y,x) is the probability that a parton level set of variables y will be measured as a set of variables x dnis the differential cross section: LO Matrix element f(q) is the probability distribution than a parton will have a momentum q Florencia Canelli - UCLA

  23. Matrix Element at D • Last result from Run I: June, 2004 • Reduced the statistical uncertainty from 5.6 to 3.6 (expected error from 7.4 to 4.4) => 2.4 times more data • Total uncertainty from 7.3 (lepton+jets CDF) to 5.3 (D0) • Run II results from D and CDF coming soon! Nature Vol 429, Page 640 Florencia Canelli - UCLA

  24. Other Matrix Element based Mtop • DLM: only a signal probability, requires b-tagging • New results with decrease JES and more data coming soon! • Ideogram: Uses same kinematic fit as D template method, and includes DLB discriminant in likelihood fit • Uses background probability Florencia Canelli - UCLA

  25. Current Best Results in Dilepton Channel • How the analyses solve the problem of under-constrained kinematics? • Integrate over 2 variables • Weight neutrino solutions • Follow template procedure 230 pb-1 S/B ~ 3/1 MPV expectation with 320pb-1Mtop ~ 9 GeV ! Florencia Canelli - UCLA

  26. Summary of Top Mass Results Florencia Canelli - UCLA

  27. W helicity

  28. W helicity • Are there new interactions at this high energy scale? • Measuring the helicity of the W boson examines the nature of the tbW vertex, and provides a stringent test of Standard Model V-A coupling W-Left-Handed fractionF- W+ Right-Handed fraction F+ W0Longitudinal fraction F0 0 -1/2 +1 +1/2 +1/2 +1/2 V-A SUPPRESSED W W b t t t b b W -1/2 +1 +1/2 Florencia Canelli - UCLA

  29. W helicity • In the Standard Model (with mb=0): • The PT of the lepton has information about the helicity of the W boson: • longitudinal: leptons are emitted perpendicular to the W (harder lepton PT) • left-handed: leptons are emitted opposite to W boson (softer lepton PT) Left-handed Longitudinal Right-handed F-= 0.3 F0= 0.7 F+=0 Florencia Canelli - UCLA

  30. Longitudinal Fraction, F0 • Likelihood analysis of cos * • Combined lepton+jet and dilepton samples: 31 events • Likelihood analysis of PT spectrum • Combined lepton+jet and dilepton samples: 70 events • Assuming F+=0 • Dominated by statistical uncertainties • Run I best result (D) 125pb-1: 0.56 +- 0.31 using ME Technique Florencia Canelli - UCLA

  31. Right Handed Fraction, F+ • Likelihood on cos* • Topological selection: 80 events • b-tagged selection: 31 events • Assuming F0=0.70 • Dominated by statistical uncertainties • Run I best result (CDF) 109pb-1: F+<0.18 @95% CL using cos* Florencia Canelli - UCLA

  32. ttbar Spin Correlations

  33. ttbar Spin Correlations • Agreement between ttbarexperimental and theoretical expectations => assume top has spin 1/2. • Since t~1.4 GeV • spin transferred to final state (decay products correlated to top quark spin). • use polarization properties of the top quark as additional observables for testing the SM and to search for New Physics. • Can be observed in single-top since it is produced 100% correlated. • Some net polarization of top quark in pair production: N(t)=N(t) but in the proper spin quantization axes a large asymmetry between like- and unlike-spin configurations can be observed • k = 0.88 SM, correlation coefficient between top- antitop spin polarizations. • D Run I: k>-0.25 @ 68% CL. • CDF Run II preliminary sensitivity study 340pb-1  =1.6, 2fb-1 =0.62. Florencia Canelli - UCLA

  34. Search for ttbar Resonances

  35. ppbar->X->ttbar • Test ttbar production from new sources such as narrow resonances • Many models of New Physics predict new particles coupled to the 3rd generation, in particular the top quark. • Better analyses techniques, from templates to ME based searches. • Use the differential cross section to reconstruct the Mttbar at parton level. • Follow template procedure for establishing limits. SM ttbar (Pythia) Red : parton level Mttbar Blue: reconstructed Mttbar Run I search of Z’ with G=1.2%M: CDF(D0): MZ’>480(560) GeV @ 95% CL Florencia Canelli - UCLA

  36. Conclusions • Top quark physics program at the Tevatron Run II is extremely rich: from QCD tests to search for New Physics. • Challenging final states: • requires to fully use detector capabilities • Method of extraction of observables are getting far more sophisticated: • making maximal use of the statistics • smarter ways to account for systematic uncertainties • We are moving from discovery to precision measurements of top quark properties. Florencia Canelli - UCLA

  37. Top Quark at APS • Top Mass in all-jets channel CDF, Georghe Lungu, Top Quark Session I, yesterday: using ME • Top Mass in dilepton channel CDF, Tuula Maki, Top Quark Session I, yesterday: using Pz ttbar • Top Mass in dilepton channel CDF: Simon Sabik, Top Quark Session I, yesterday: using neutrino weighting • Top Mass in lepton+jets channel CDF: Jean-Francois Arguin, Top Quark Session I, yesterday: using 2-D template • Top Mass in lepton+jets CDF/LHC: James Lamb, Top Quark Session I, yesterday: using decay length • Top Mass in lepton+jets D0: Philipp Schienferdecker, Top Quark Session II, today: using D0 matrix element in Run II • Top Mass in lepton+jets D0: Robert Harrington, Top Quark Session II, today: using D0 matrix element in Run II + b-tagging • Top Mass in dilepton D0: Petr Homola, Top Quark Session II, today: neutrino weighting • Top Mass in lepton+jets D0: Martjin Mulders, Top Quark Session II, today: matrix element Ideogram • Top Mass in dilepton D0: Jeff Temple, Top Quark Session II, today: neutrino weighting • X->ttbar at CDF: Top Quark Session III, Brandon Parks, Valentin Necula, NN and ME technique • W-helicity: Top Quark Session III, Bryan Gmyrek, cos(theta*) Florencia Canelli - UCLA

  38. Mtop Measurement in lepton+jets Channel • Larger branching ratio • Reasonable Signal/Background • Over-constrained kinematics • Signature • Two b quarks • Two light quarks • High pT lepton • Neutrino (undetected) • Px and Py from ET conservation • Pz constrained by kinematics Leading 4 jets combinatorics • 12 possible jet-parton assignments • 6 with 1 b-tag • 2 with 2 b-tags ISR + FSR: Extra jets from initial/final state gluons • Typical event selection: • One high PT lepton (20 GeV) • 4 or more jets (>15 GeV) • ET (>20 GeV) • b-tagging (optional) Two different techniques: Template and Matrix Element based Florencia Canelli - UCLA

  39. Mtop Measurement in Dilepton Channel • Less statistics • Excellent S/B • Underconstrained kinematics: need to assume knowledge of some quantity • Less combinatorics: 2 jets • Smaller jet systematics • Signature: • Two b quarks • Two high PT leptons • Two neutrinos • Typical event selection: • One high PT lepton (>15 GeV) • Oppositely charged high PT lepton or isolated track (>15 GeV) • Two or more high PT jets (>20 GeV) • ET (>25 GeV) • Backgrounds: • Diboson, Drell-Yan, Z->tautau, W+jets (fake lepton) Florencia Canelli - UCLA

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